Known circuit-breaker pole parts can be integrated in a medium-voltage to high-voltage circuit-breaker arrangement, such as medium-voltage circuit-breakers rated between 1 and 72 kV of a high current level. These specific circuit breakers interrupt the current by generating and extinguishing the arc in a vacuum. Inside the vacuum chamber a pair of electrical switching contacts is arranged. Modern vacuum circuit-breakers tend to have a longer life time than former air, oil circuit-breakers. Although, vacuum circuit-breakers replaced air, oil circuit-breakers, the present disclosure is not only applicable to vacuum circuit-breakers but also for air, oil circuit-breakers or modern SF6 circuit-breakers having a chamber filled with sulfurhexafluoride gas instead of vacuum.
For actuating a circuit-breaker, a magnetic actuator with a high force density is used with moves one of the electrical contacts of a vacuum interrupter for a purpose of electrical power interruption. Therefore, a mechanical connection between a movable armature of the magnetic actuator and the movable electrical contact inside the vacuum interrupter insert is provided.
The document DE 10 2004 060 274 A1 discloses a method for producing a circuit-breaker pole part for a medium voltage or high voltage circuit-breaker. A vacuum interrupter is embedded in an insulating material and encapsulated with said material. The vacuum interrupter itself substantially comprises an insulator housing which can be cylindrical and which is closed at the ends in order to form an inner vacuum chamber. The vacuum chamber contains a fixed electrical contact and a corresponding movable electrical contact forming an electrical switch. A folding bellows is arranged on the movable electrical contact side and permits a movement of the movable electrical contact over the current feed line within the vacuum chamber. As mentioned, a vacuum is inside the vacuum interrupter in order to quench as rapid as possible the arc produced during the switching-on or switching-off action.
The vacuum interrupter inside the insulating sleeve is fully encapsulated by a synthetic material, mostly plastic material, in order to increase the external dielectric strength of the vacuum interrupter. Furthermore, the synthetic material serves as a compensation material for the purpose of compensating for different coefficient of thermal expansion between the vacuum interrupter surface and the surrounding insulating sleeve. This additional function of the intermediate layer avoids possible initiation of cracks.
During the manufacturing process of the circuit-breaker pole part two external electrical terminals are mounted in the wall section of the insulating sleeve in a first step. In a second step, the pre-mounted interrupter insert is dipped into a liquid rubber solution forming the above-mentioned intermediate layer. In a third step, the external insulating sleeve is produced in a plastic injection-molding process by the vacuum interrupter being encapsulated with plastic material. During encapsulating the interrupter by molding under a high process temperature, the liquid rubber solution vulcanizes and forms the intermediate compensating layer as described above. For the last productions step of vulcanization a heated molded form is necessary.